1. Field of the Invention
The present invention relates to an apparatus for manufacturing flat glass wherein the glass is formed while being supported on a surface of a pool of molten metal following delivery of the glass onto the molten metal over a threshold or other refractory support from a glassmaking furnace. More particularly, this invention relates to a threshold or canal of a molten glass delivery facility for supporting molten glass during its delivery onto the pool of molten metal.
2. Brief Description of the Prior Art
It is known that molten glass can be delivered onto molten metal and formed into a continuous ribbon or sheet of glass according to the teachings of Heal, U.S. Pat. No. 710,357; of Hitchcock, U.S. Pat. No. 789,911; of Pilkington, U.S. Pat. No. 3,083,551 and of Edge and Kunkle, U.S. Pat. No. 3,843,346. In all of the prior art, molten glass is delivered over some rigid element usually a refractory member onto molten metal. In the practice disclosed by Pilkington, the molten glass is delivered through a long, narrow canal and over a lip from which molten glass falls freely onto molten metal and spreads outwardly upon it to form a body of floating glass which is advanced along the molten metal to form a continuous ribbon of glass.
In the patents of Heal, Hitchcock and Edge and Kunkle, molten glass is delivered over a refractory support along a substantially horizontal path, that is, it is not permitted to fall freely. The path taken by the glass may be either a perfectly horizontal path or a downwardly sloping path. After delivery, the glass advances as a wide stream of molten glass onto and along the molten metal. In the method and apparatus of Edge and Kunkle, a refractory threshold is provided over which molten glass is delivered as described in U.S. Pat. No. 3,884,665. The refractory threshold is preferably an element having an upwardly facing convex surface for supporting molten glass during its delivery from the glassmaking furnace to the glass forming chamber. In general, the threshold acts as a dividing member or wall member between the glassmaking furnace and the forming chamber in addition to being a support for the molten glass during delivery.
Several recent patents describe particular thresholds and their arrangements with respect to glassmaking furnaces and associated glass forming chambers as used in the apparatus generally taught by Edge and Kunkle in U.S. Pat. No. 3,843,346. These include U.S. Pat. No. 3,854,922 to Sensi and Wehner; U.S. Pat. No. 3,898,069 to Cerutti and Gulotta and U.S. application Ser. No. 549,214 to Cerutti and Gulotta now U.S. Pat. No. 3,986,857.
With particular reference to U.S. Pat. No. 3,898,069 to Cerutti and Gulotta, it is appreciated that a threshold may be mounted at least partially within an impervious metal casing housing a forming chamber and that a refractory threshold may be mounted adjacent to a refractory liner within such a casing so that the threshold may form a part of the container for containing a pool of molten metal, such as tin, within the forming chamber.
The present applicant has devised an improved threshold or other glass support whereby the risk of transpiration of gases from outside a forming chamber into it through the threshold may be reduced or eliminated.